KDE has its own office suite, called Calligra -- earlier called KOffice -- that happens to be an excellent software, and in many ways, particularly the user interface, it is better than the more popular LibreOffice / OpenOffice.org. Unfortunately, it has not been easily available for Windows till now, bring offered only as a part of the larger KDE for Windows.
The Calligra suite consists of a number of applications; Words, the word processor; Tables, the spreadsheet; Stage, the presentation software; Flow for diagrams and flowcharts; Krita, for raster image editing and painting; Karbon for working with vector graphics; and Braindump a mind-mapping / whiteboard / planning software. And these are only the ones available on Windows, on Linux you also have Kexi, for databases; and Plan for project management. It is full-fledged indeed.
What sets Calligra apart from other suites is its interface, and the great customizability it offers. Monitors are mostly wide-screen, and documents are mostly portrait, its not a good match on the best of days, however most office suites further take up a large amount of vertical space by throwing in layers of toolbars. Calligra applications instead have vertical panels on the left and right giving your documents more space. The interface is endlessly customizable, you can pretty much move any panel and relocate it to another part of the interface, or even out of the window. You can make good use of multiple monitors and best of all you can set up a shortcut for any action.
Calligra Suite is a welcome addition to the Windows world, and while the current version is just an unstable beta -- and one that we had quite some trouble getting to run on our system -- it has a bright future ahead, especially since it is also headed to mobiles and tablets.
You can find out more about Calligra from here and can download it from here.